Automatic idle speed controller

ABSTRACT

A speed controller to maintain a constant idle speed in an internal combustion engine experiencing variable accessory loads. Basic apparatus includes a sensor-modulator assembly and a throttle actuator means. The sensor-modulator provides a vacuum signal to the throttle actuator means based on intake manifold vacuum and throttle plate angle. The throttle actuator means comprises a vacuum motor connected to the throttle lever so that the idle speed of the engine may be kept constant by moving the throttle blade in response to the engine load affects on the engine manifold vacuum.

I 1 Oct. 30, 1973 United States Patent 11 1 Harrison AUTOMATIC IDLE SPEED CONTROLLER Primary ExaminerC. J. Husar Inventor: Robert S. Harrison, Detroit, Mich. Atwmey' Keith Zerschling at Assignee: Ford Motor Company, Dearborn,

[57] ABSTRACT A speed controller to maintain a constant idle speed in Mich.

[ Filed: 23! 1971 an internal combustion engine experiencing variable {2]} App], N0; 211,517 accessory loads. Basic apparatus includes a sensormodulator assembly and a throttle actuator means.

modulator provides a vacuum signal to the uator means based on intake manifold vacuum and throttle plate angle. The throttle actuator means comprises a vacuum motor connected to the throttle lever so that the idle speed of the en gine may be kept constant by moving the throttle blade in regine manirt mu e m mm Tm ZMR l m S M H T 1 3 N 2 8A u t mm 2 m 5% mT GA a": rT an" .NS h e "6 D HM, E Mme T "Us I. cm W l sponse to the engine load affects on the en fold vacuum.

3,252,450 5/1966 Dietrich et 123 103 R,

1 03 3,682,148 8/1972 l -lamson 23/1 R 12 Chums, 4 Drawing sum PAIENIEDncI 30 ms 3.7683150 SHEET 3 OF 3 FIG.3

AUTOMATIC IDLE SPEED CONTROLLER BACKGROUND AND SUMMARY OF THE INVENTION Engines of todays automobiles are required to provide power for numerous accessories as well as for comotion. Several of these accessories make substantial power demands on the engine when the engine is idling and developing its minimum power. For example, in typical city driving the air conditioner is often operating when the vehicle is idling and while other accessories are demanding power. In a parking situation the power steering requires significant engine power and the result, unless compensation is made, is that the engine may operate roughly or perhaps stall. This invention provides a means to maintain an essentially constant idle speed irrespective of the momentary engine loads.

Control of engine idle speeds gains further importance as a factor reducing engine emissions.

This invention provides an idle speed controller which is responsive to both intake manifold vacuum and the throttle blade angle. By sensing these two characteristics of engine operation, the invention further provides an idle speed controller which senses its previous response to determine the next response.

The invention also provides means by which idle speed can be prevented from dropping below a certain predetermined magnitude and by which engine roughness and stalling due to large accessory power requirements during idle is reduced or prevented.

This invention further provides a means to prevent the progressively increasing idle speed resulting from initial engine wear-in or break-in. Finally, this invention provides idle speed controller which is easily adjustable, reliable in operation and economical to produce.

An idle speed controller system constructed in accordance with this invention includes a sensor-modulator, a throttle actuator means comprising a vacuum motor connected to the throttle plate of the engine carburetor and passage means communicating and interconnecting the engine intake manifold, the sensor-modulator assembly and the throttle actuator. The sensormodulator assembly includes a valve movable in response to changes in both intake manifold vacuum and throttle plate angle to progressively open and close atmospheric air bleed. The valve when opening decreases the magnitude of the vacuum signal communicated to the vacuum motor.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The idle speed controller system, shown in FIG. 1 of the drawings, consists primarily of a sensor-modulator 11 and a throttle actuator means 13. The sensormodulator is communicated with a source of intake manifold vacuum through a passage 15. The throttle actuator is communicated with the source of intake manifold vacuum through passage 17. Passage 19 interconnects passage 17 with a vacuum bleed located within the sensor-modulator. Follower lever 21 of the sensor-modulator is positioned by or follows throttle lever 23, which is fixed relative to the carburetor throttle shaft 22 and throttle blade 24. The sensormodulator responds to intake manifold vacuum through passage 15 and the throttle blade position as indicated by lever 21 to vary the vacuum magnitude within portion 17b of passage 17. The throttle actuator means 13 is responsive to the vacuum signal within portion 17b and positions throttle lever 23 within carburetor barrel 26 in accordance with this vacuum signal.

FIG. 3 of the drawings illustrates in detail sensormodulator 11. It includes a housing 41 that defines an enclosure 43. An arm 44 is pivotally mounted to the housing by shaft 45 and is biased counterclockwise or upwardly by leaf spring 47 that engages enclosure cover 49. Pivotally mounted to an eccentric pin 51 or arm 44 is a second arm 53 that is biased upwardly or counterclockwise by coil spring 55. The enclosure is open to atmospheric pressure through passage 57. It is preferably connected to a source of clean atmospheric pressure such as the exterior of the engine air cleaner.

A vacuum motor 59 is formed in housing 41 and an upper cover 61. It includes a flexible diaphragm 63 defining a vacuum chamber 65 and an atmospheric chamber 67. A plunger 69 is secured to the diaphragm and engages the upper side of the free end of arm 53. The plunger is biased downwardly (according to FIG. 3) by compression spring 71 toward a minimum volume atmospheric chamber. The vacuum chamber is communicated to a source of intake manifold vacuum through passage 73. The atmospheric chamber is vented through passage 75.

Engaging arm 53 near its pivotal connection with arm 44 is a ball 77 of check valve assembly 79. When the valve is closed the ball seats against the periphery of orifice 81 and prevents communication between the atmospheric pressure in the compartment 43 and the manifold vacuum within passage 19. A spool 83 is movable within a bore 85 and is biased downwardly (according to FIG. 3) by compression spring 87 which tends to push ball 77 toward an open position in opposition to the vacuum pressure. The spool ends 89 are star shaped so as to permit free airflow thorugh the spool from passage 19 to orifice 81.

Abutment lever 21 (shown in FIGS. 1 and 2) is secured to an end of shaft 45 which protrudes from the housing 41. The lever is biased by leaf spring 47 upwardly into engagement with the throttle lever portion 91 for about the first 10 of throttle opening movement. A'tab 93 of lever 21 engages housing 41 to prevent follower lever 21 from further counterclockwise movement (as viewed in FIG. 1). The throttle lever 23 is biased by spring 95 toward engagement with lever 21 and toward a closed throttle position. Lever 21 simply follows lever 23 during final closing or initial opening movements of the throttle plate. An adjustment screw 97 provides a means to vary the effective length of throttle lever 23 or, alternatively stated, provides a means to vary the position of throttle lever 23 relative to lever 21 of the sensor-modulator 11.

The throttle actuator means 13 comprises a vacuum motor within housing 99 supported by bracket 101 to the carburetor flange 103. A flexible diaphragm 105 divides the housing enclosure into a vacuum chamber 107 and a vented chamber 109. A plunger 111 is secured to and displaced by diaphragm 105 in response to changes in vacuum signal within passage 17b. The protruding end of the plunger engages throttle lever 23 at tab 113. A compression spring 115 urges the plunger toward a maximum protracted position.

A fast idle means 25 is shown schematically in FIG. 1. It comprises a thermosensitive bimetal spring 27 connected to a metering rod 29 which operates within an orifice 31 and provides a variable bleed to the atmosphere from the vacuum passage 15. When the engine is warm the orifice 31 is fully closed. Similarly to the sensor-modulator air bleed, it may be joined to a source of clean air, such as the carburetor air cleaner.

An anti-diesel means 33 is shown schematically in FIG. 1. A solenoid 35 opens valve 37 when the engine ignition is turned off" to communicate a vacuum reservoir 39 and the vacuum motor 13. This causes the vacuum motor to close completely or very nearly completely throttle blade 24 within the carburetor barrel to prevent air flow and dieseling often associated with such post ignition air flow.

Line restrictors 117 and 119 are inserted within passage 17 to increase the sensitivity of the system. For example, without restrictor 117 the amount of air that would have to be bled through valve 79 to provide effective modulation would be much greater. Similarly, without restrictor 119 the effect of the anti-diesel means 33 would be largely lost.

OPERATION It has been found that intake manifold vacuum pressure at idle or near idle speeds varies essentially inversely to the engine load. The idle speed controller system described in the foregoing paragraphs senses the intake manifold vacuum, takes into account the throttle blade opening and determines whether the throttle blade opening should be increased, decreased or unchanged.

For example, assume that the vehicle engine is idling and that the air conditioner compressor begins operation. The intake manifold vacuum pressure drops in response to the increased load. Vacuum motor 59 of the sensor-modulator 11 experiences a similar vacuum pressure drop causing compression spring 71 to displace plunger 69 downwardly (according to FIG. 3). Arm 33 is then displaced downwardly or clockwise about eccentric pin 51 causing ball 71 to drop and open orifice 81 of valve 79. Atmospheric air is bled from enclosure 43 through orifice 81 into passage 19 to further reduce the vacuum signal within portion 17b of passage 17. The reduced vacuum signal within portion 17b of passage 17 is also experienced by vacuum chamber 107 of the throttle actuator 13 causing compression spring 115 to displace plunger 111 leftwardly (according to FIG. 1) and displace throttle lever 23 counterclockwise to increase the opening of the carburetor throttle blade 24 and to provide increased power to operate the air conditioner compressor. Engine r.p.m. will drop during the short response period but, relative to an engine without a controlled idle system, will be very nearly constant. Lever 21 of the sensor-modulator l1 follows throttle lever 23 and is thus displaced in a counterclockwise direction by the force of leaf spring 47 (shown in FIG. 3). Arm 44, fixed relative to lever 21,

moves counterclockwise displacing pin 51 and the attached end of arm 53 upwardly. If the throttle actuator response was sufficient, ball 77 is again seated in orifice 81 and the atmospheric air bleed is closed. If the throttle actuator response is not sufficient the valve 79 will not be fully closed and the entire cycle will be repeated. It, thus, may be seen that the system is responsive to changes in both engine intake manifold vacuum and throttle blade position to provide increased power to operate engine accessories and maintain an essentially constant engine idle speed.

When the engine is cold, the bimental spring 27 of fast idle means 25 (shown in FIG. 1) supports metering rod 29 out of orifice 31 to provide an atmospheric air bleed to passage 15. This causes a reduction in vacuum pressure experienced by vacuum motor 59 of the sensor-modulator 11. The system responds as described previously causing the opening or increased opening of throttle blade 24 and a corresponding increase in engine idle speed.

When the engine ignition is turned off the solenoid 35 of anti-diesel means 33 (shown in FIG. 1) is deenergized and the valve 37 is spring biased to an open position, communicating vacuum reservoir 39 and vacuum chamber 107 of the throttle actuator 13. This causes the flexible diaphragm to move rightwardly withdrawing the plunger 111 and closing the throttle blade 24 to reduce the engine tendency to diesel."

Modifications and alterations will occur to those skilled in the art which are included in the scope of the following claims.

I claim:

1. An idle speed controller system for an internal combustion engine having an intake manifold and a carburetor including a throttle plate, said controller constructed to open said throttle plate in response to a decrease in intake manifold vacuum,

a sensor-modulator assembly,

motion transfer means interconnecting the throttle plate and the sensor-modulator assembly, a vacuum motor, passage means communicating said intake manifold,

sensor-modulator assembly and vacuum motor,

said sensor-modulator assembly including a valve means movable in response to changes in both intake manifold vacuum and throttle blade angle to progressively open and close atmospheric air bleed means, the opening of said valve means decreasing the magnitude of the vacuum signal communicated to said vacuum motor,

means connecting said throttle plate and said vacuum motor constructed to open the throttle plate in response to a decrease in vacuum signal to said vacuum motor.

2. An idle speed controller system for an internal combustion engine including a carburetor having at least one barrel formed therein, a throttle plate positioned within said barrel, a shaft pivotally supporting said throttle plate within said barrel, said throttle plate being movable to increase and decrease restriction of the barrel, and a lever secured to the shaft movable with the throttle plate,

an intake manifold in communication with said carburetor barrel,

said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum,

said idle speed controller system comprising a sensor-modulator assembly,

a vacuum motor,

passage means communicating said sensormodulator assembly, said vacuum motor and said source of intake manifold vacuum,

said sensor-modulator assembly including a valve means having a movable element which when open permits atmospheric air to bleed into said passage means,

means positioning said movable valve element responsive to intake manifold vacuum and throttle blade angle, an increase in manifold vacuum tending to close said valve means, an opening movement of said throttle plate tending to close said valve means,

said vacuum motor having a movable element spring biased toward a maximum extending position, an increase in vacuum signal to said motor causing a withdraw of said movable element,

said vacuum motor being connected to the throttle lever to increase the opening of the throttle blade in response to a decrease in vacuum signal and decrease the opening of the throttle blade in response to an increase in the vacuum signal,

said vacuum signal varying in response to the vacuum within said intake manifold and the amount of atmospheric air bled into said passage through said sensor-modulator valve means.

3. An idle speed controller system for an internal combustion engine including a carburetor having at least one barrel formed therein and a throttle plate pivotally mounted within said barrel,

an intake manifold in communication with said carburetor barrel,

said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum,

said idle speed controller system comprising a sensor-modulator assembly,

a first vacuum motor,

passage means communicating said sensormodulator assembly, said vacuum motor and said source of intake manifold vacuum,

said sensor-modulator comprising a housing,

a first lever arm pivotally mounted to said housing movable about a first axis fixed relative to said housing, v

a second lever arm pivotally connected to said first lever arm movable about a second axis fixed relative to said first lever arm and parallel to and spaced from said first axis,

means operably connecting said first lever arm to said throttle plate to move said throttle plate and said first lever means simultaneously for a portion of the initial opening and final closing travel of said throttle plate,

valve means positioned in said housing having a movable element biased into engagement with said second lever means, said valve progressively venting said passage means to bleed atmospheric air thereto and to modulate the vacuum signal to said first vacuum motor,

said vacuum signal being defined as the intake manifold vacuum pressure from said source of intake manifold vacuum modulated by said valve means of said sensor assembly,

a second vacuum motor positioned in said housing having movable means responsive to changes in intake manifold vacuum and constructed to move said second lever arm about said second axis,

said first vacuum motor means being responsive to said vacuum signal and operably connected to said throttle plate to open and close said throttle plate in response to changes in said vacuum signal.

4. An idle speed controller according to claim 3,

second passage means communicating said second vacuum motor and the source of intake manifold vacuum,

second valve means in said second passage means constructed to open and close a second atmospheric air bleed,

thermosensitive means responsive to engine temperature,

means operably connecting said second valve means and said thermosensitive means,

whereby said vacuum motor signal to said first vacuum motor is a function of intake manifold vacuum, throttle plate angle and engine temperature.

5. An idle speed controller according to claim 3,

a vacuum reservoir communicating with said first vacuum motor means,

third valve means between said vacuum reservoir and said first vacuum motor constructed to open and close said reservoir to said first vacuum motor means,

a spring biased solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed.

6. An idle speed controller according to claim 4,

a vacuum reservoir communicating with said first vacuum motor means,

third valve means between said vacuum reservoir and said first vacuum motor constructed to open and close said reservoir to said first vacuum motor means,

a solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed,

7. An idle speed controller system for an internal combustion engine including:

a carburetor having at least one barrel formed therein and a throttle plate pivotally mounted within said barrel,

an intake manifold in communication with said carburetor barrel,

said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum,

said idle speed controller system comprising a sensor-modulator assembly,

a first vacuum motor,

passage means communicating said sensormodulator assembly, said vacuum motor and said source of intake manifold vacuum,

said sensor-modulator comprising a housing,

a first lever arm pivotally mounted to said housing movable about a first axis fixed relative to said housing,

a second lever arm pivotally connected to said first lever arm movable about a second axis fixed relative to said first lever arm and parallel to and spaced from said first axis,

means operably connecting said first lever arm to said throttle plate to move said throttle plate and said first lever means simultaneously for an initial portion of the range of travel of said throttle plate,

first valve means positioned in said housing having a movable element biased into engagement with said second lever means, said first valve means progressively venting said passage means to bleed atmospheric air thereto and to modulate the vacuum signal to said first vacuum motor,

said vacuum signal being defined as the intake manifold vacuum pressure from said source of intake manifold vacuum modulated by said first valve means of said sensor assembly,

a second vacuum motor positioned in said housing having movable means responsive to changes in intake manifold vacuum and constructed to move said second lever arm about said second axis,

a decrease in intake manifold vacuum causing said second vacuum motor means to displace said second lever arm toward a position tending to open said valve means, an increase in intake manifold vacuum tending to close said valve means,

said first vacuum motor means being responsive to said vacuum signal and operably connected to said throttle plate to increase the opening and angle of said throttle plate upon a decrease in vacuum signal magnitude and to decrease the opening and angle of said throttle plate upon an increase in vacuum signal magnitude.

8. An idle speed controller according to claim 7,

second passage means communicating said second vacuum motor and the source of intake manifold vacuum,

second valve means in said second passage means constructed to open and close an atmospheric air bleed,

thermosensitive means responsive to engine temperature,

means operably connecting said second valve means and said thermosensitive means,

whereby said vacuum motor signal to said first vacuum motor is a function of intake manifold vacuum, throttle plate angle and engine temperature.

9. An idle speed controller according to claim 7,

a vacuum reservoir communicating with said first vacuum motor means,

third valve means between said vacuum reservoir and said first vacuum motor means,

a solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed,

whereby the vacuum from the reservoir communicated to the first vacuum motor means upon opening the engine ignition circuit causes the throttle plate to be displaced to its most nearly closed position.

10. In a carburetor having a throttle lever secured to the throttle plate and movable therewith and first spring means biasing the throttle plate toward a closed position,

an idle speed controller system according to claim 7,

said sensor-modulator assembly having a follower lever fixed to said first lever arm to move therewith,

second spring means biasing said first lever arm and said input follower toward abutting engagement with the throttle lever,

said second spring means opposing the first spring means.

11. An idle speed controller system according to claim 10,

the axes of rotation of the throttle lever and said first lever arm being colinear. 12. An idle speed controller system according to claim 10,

ward engagement with said movable member. 

1. An idle speed controller system for an internal combustion engine having an intake manifold and a carburetor including a throttle plate, said controller constructed to open said throttle plate in response to a decrease in intake manifold vacuum, a sensor-modulator assembly, motion transfer means interconnecting the throttle plate and the sensor-modulator assembly, a vacuum motor, passage means communicating said intake manifold, sensormodulator assembly and vacuum motor, said sensor-modulator assembly including a valve means movable in response to changes in both intake manifold vacuum and throttle blade angle to progressively open and close atmospheric air bleed means, the opening of said valve means decreasing the magnitude of the vacuum signal communicated to said vacuum motor, means connecting said throttle plate and said vacuum motor constructed to open the throttle plate in response to a decrease in vacuum signal to said vacuum motor.
 2. An idle speed controller system for an internal combustion engine including a carburetor having at least one barrel formed therein, a throttle plate positioned within said barrel, a shaft pivotally supporting said throttle plate within said barrel, said throttle plate being movable to increase and decrease restriction of the barrel, and a lever secured to the shaft movable with the throttle plate, an intake manifold in communication with said carburetor barrel, said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum, said idle speed controller system comprising a sensor-modulator assembly, a vacuum motor, passage means communicating said sensor-modulator assembly, said vacuum motor and said source of intake manifold vacuum, said sensor-modulator assembly including a valve means having a movable element which when open permits atmospheric air to bleed into said passage means, means positioning said movable valve element responsive to intake manifold vacuum and throttle blade angle, an increase in manifold vacuum tending to close said valve means, an opening movement of said throttle plate tending to close said valve means, said vacuum motor having a movable element spring biased toward a maximum extending position, an increase in vacuum signal to said motor causing a withdraw of said movable element, said vacuum motor being connected to the throttle lever to increase the opening of the throttle blade in response to a decrease in vacuum signal and decrease the opening of the throttle blade in response to an increase in the vacuum signal, said vacuum signal varying in response to the vacuum within said intake manifold and the amount of atmospheric air bled into said passage through said sensor-modulator valve means.
 3. An idle speed controller system for an internal combustion engine including a carburetor having at least one barrel formed therein and a throttle plate pivotally mounted within said barrel, an intake manifold in communication with said carburetor barrel, said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum, said idle speed controller system comprising a sensor-modulator assembly, a first vacuum motor, passage means communicating said sensor-moduLator assembly, said vacuum motor and said source of intake manifold vacuum, said sensor-modulator comprising a housing, a first lever arm pivotally mounted to said housing movable about a first axis fixed relative to said housing, a second lever arm pivotally connected to said first lever arm movable about a second axis fixed relative to said first lever arm and parallel to and spaced from said first axis, means operably connecting said first lever arm to said throttle plate to move said throttle plate and said first lever means simultaneously for a portion of the initial opening and final closing travel of said throttle plate, valve means positioned in said housing having a movable element biased into engagement with said second lever means, said valve progressively venting said passage means to bleed atmospheric air thereto and to modulate the vacuum signal to said first vacuum motor, said vacuum signal being defined as the intake manifold vacuum pressure from said source of intake manifold vacuum modulated by said valve means of said sensor assembly, a second vacuum motor positioned in said housing having movable means responsive to changes in intake manifold vacuum and constructed to move said second lever arm about said second axis, said first vacuum motor means being responsive to said vacuum signal and operably connected to said throttle plate to open and close said throttle plate in response to changes in said vacuum signal.
 4. An idle speed controller according to claim 3, second passage means communicating said second vacuum motor and the source of intake manifold vacuum, second valve means in said second passage means constructed to open and close a second atmospheric air bleed, thermosensitive means responsive to engine temperature, means operably connecting said second valve means and said thermosensitive means, whereby said vacuum motor signal to said first vacuum motor is a function of intake manifold vacuum, throttle plate angle and engine temperature.
 5. An idle speed controller according to claim 3, a vacuum reservoir communicating with said first vacuum motor means, third valve means between said vacuum reservoir and said first vacuum motor constructed to open and close said reservoir to said first vacuum motor means, a spring biased solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed.
 6. An idle speed controller according to claim 4, a vacuum reservoir communicating with said first vacuum motor means, third valve means between said vacuum reservoir and said first vacuum motor constructed to open and close said reservoir to said first vacuum motor means, a solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed,
 7. An idle speed controller system for an internal combustion engine including: a carburetor having at least one barrel formed therein and a throttle plate pivotally mounted within said barrel, an intake manifold in communication with said carburetor barrel, said carburetor barrel downstream of said throttle plate and the intake manifold being defined as a source of intake manifold vacuum, said idle speed controller system comprising a sensor-modulator assembly, a first vacuum motor, passage means communicating said sensor-modulator assembly, said vacuum motor and said source of intake manifold vacuum, said sensor-modulator comprising a housing, a first lever arm pivotally mounted to said housing movable about a first axis fixed relative to said housing, a second lever arm pivotally connected to said first lever arm movable about a second axis fixed relative to said first lever arm and parallel to and spaced from said first axIs, means operably connecting said first lever arm to said throttle plate to move said throttle plate and said first lever means simultaneously for an initial portion of the range of travel of said throttle plate, first valve means positioned in said housing having a movable element biased into engagement with said second lever means, said first valve means progressively venting said passage means to bleed atmospheric air thereto and to modulate the vacuum signal to said first vacuum motor, said vacuum signal being defined as the intake manifold vacuum pressure from said source of intake manifold vacuum modulated by said first valve means of said sensor assembly, a second vacuum motor positioned in said housing having movable means responsive to changes in intake manifold vacuum and constructed to move said second lever arm about said second axis, a decrease in intake manifold vacuum causing said second vacuum motor means to displace said second lever arm toward a position tending to open said valve means, an increase in intake manifold vacuum tending to close said valve means, said first vacuum motor means being responsive to said vacuum signal and operably connected to said throttle plate to increase the opening and angle of said throttle plate upon a decrease in vacuum signal magnitude and to decrease the opening and angle of said throttle plate upon an increase in vacuum signal magnitude.
 8. An idle speed controller according to claim 7, second passage means communicating said second vacuum motor and the source of intake manifold vacuum, second valve means in said second passage means constructed to open and close an atmospheric air bleed, thermosensitive means responsive to engine temperature, means operably connecting said second valve means and said thermosensitive means, whereby said vacuum motor signal to said first vacuum motor is a function of intake manifold vacuum, throttle plate angle and engine temperature.
 9. An idle speed controller according to claim 7, a vacuum reservoir communicating with said first vacuum motor means, third valve means between said vacuum reservoir and said first vacuum motor means, a solenoid connected to said third valve means opening said third valve means when the engine ignition circuit is opened and closing said third valve means when the circuit is closed, whereby the vacuum from the reservoir communicated to the first vacuum motor means upon opening the engine ignition circuit causes the throttle plate to be displaced to its most nearly closed position.
 10. In a carburetor having a throttle lever secured to the throttle plate and movable therewith and first spring means biasing the throttle plate toward a closed position, an idle speed controller system according to claim 7, said sensor-modulator assembly having a follower lever fixed to said first lever arm to move therewith, second spring means biasing said first lever arm and said input follower toward abutting engagement with the throttle lever, said second spring means opposing the first spring means.
 11. An idle speed controller system according to claim 10, the axes of rotation of the throttle lever and said first lever arm being colinear.
 12. An idle speed controller system according to claim 10, said first vacuum motor including a movable member engagable with the throttle lever, the first spring means biasing the throttle lever toward engagement with said movable member. 